Numerical Simulations of the Aerodynamic Characteristics of

Circulation Control Wing Sections

A Thesis Proposal

ByYI LIU

Advisor: Dr. L.N.SANKAR

Supported by NASA

OVERVIEW• Motivation and Objectives• Background and Circulation Control Concept• Mathematical and Numerical Formulation

• Solution Procedure• Initial and Boundary Conditions

• Results and Discussion• Code Validation for a NACA 0012 Wing• Steady Blowing Results • Pulsed Jet Results

• Preliminary Conclusions• Proposed Work

Motivation and Objectives• Noise pollution from the large aircraft has

become a major problem that needs to be solved.

• A major source of large aircraft airframe noise during take-off and landing is the high-lift system - namely flaps, slats, flap-edges and gaps.

• An alternative to conventional high-lift systems is the Circulation Control Wing (CCW) technology.

Circulation Control Wing Concept

• Circulation Control Aerodynamics: In this approach a tangential jet is blown over a highly curved aerodynamic surface (the Coanda surface) to increase or modify the aerodynamic forces and moment with few or no moving surfaces.

• Fig. 1 (Paper by Robert Englar) shows the traditional Circulation Control Wing Airfoil with a rounded trailing edge.

Advanced Circulation Control Wing Airfoil

• Use a small trailing edge flap with a large-radius arc upper surface and a flat low surface.

• Flap can be deflected 00 < f < 900.

• During cruise, f = 00, leading to a conventional airfoil shape with a sharp trailing edge.

Benefits of the CCW Wing

Pneumatic Airfoils Simplify Wing Complexity (Paper by Robert Englar)

• Experimental studies show that very high lift coefficient values (as high as 8.5 at =0) can be achieved by CCW technology (Englar).

• Numerical studies of the dynamic stall characteristics of the Circulation Control Wing airfoil have also been done (Shrewsbury).

• Aeroacoustic characteristics of CCW configurations are being studied at GTRI (Ahuja and Munro).

• Several synthetic and pulsed jet studies have also been reported (Wygnansky, Lorber, Wake, Hassan and Oyler). These studies have primarily focused on the boundary layer separation control or conventional rounded trailing edge CCW airfoils.

Related Research Work

• Three-dimensional compressible unsteady Reynolds Averaged Navier-Stokes equations are solved in a strong conservation form on curvilinear coordinates.

• This solver can be used in both a 2-D mode and a 3-D mode in this study for different applications.

• The scheme is second or fourth order accurate in space and first order accurate in time.

• Baldwin-Lomax and Spalart-Allmaras one-equation turbulence models have been used.

• The jet slot location, slot size, blowing velocity and direction of blowing can easily be varied in the analysis.

Mathematical and Numerical Formulation

Initial and Boundary Conditions

• Initial flow conditions are set to free stream values inside the flow field.

• Boundary Conditions

• Outer Boundary

• Solid Surface Boundary

• Wake Cut Boundary

• Jet Slot Exit Boundary

• The driving parameter for jet blowing is the momentum coefficient, Cdefined as follows:

Jet Slot Boundary Conditions

2

jet

V21*S

m*VC

Where jetjetjet A*Vm is the mass flow rate of jet flow

• We specify C orientation of the jet and the total temperature of jet.

• Other quantities such as pressure and density are found by extrapolation and /or Ideal Gas Law.

Code Validation 34% SPAN

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CHORD

Cp

Upper- ExpLower -ExpLower CalUpper Cal

66% SPAN

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CHORD

Cp

Upper ExpLower ExpLower CalUpper Cal

85% SPAN

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CHORD

Cp

Upper ExpLower ExpLower CalUpper Cal

• The figures are the Cp distribution at three span locations of a small aspect-ratio wing made of NACA 0012 airfoil sections.• The results are in good agreement with the measured data (from Bragg and Spring) except near the tip region where increased grid resolution is needed.

The CCW Airfoil

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Jet Slot Location

30 degree integral flap

Flow Conditions• P = 14.2 psia = 0.9324 atm

• = 0.00225 slugs/ft3 = 1.1596 kg/m3

• V = 94.3 ft/sec = 28.743 m/s

• M = 0.0836, Re = 0.395 * 106

• Chord of the Airfoil : C = 8” = 0.20 m

• Jet Slot Height : h = 0.015” = 0.0004 m

• Jet slot is located at x/c = 88.75% on the upper side of the airfoil.

• These values closely match the test conditions.

Steady Blowing ResultsComputed vs. Measured Variations of Lift Coefficient with

Momentum Coefficient

0

1

2

3

4

5

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

C

Cl

Cl, Computed

Cl, Measured

Angle of Attack 0 degrees, Integral Flap at 30 degrees

Variation of Lift Coefficient with Angle of Attack

0

1

2

3

4

-2 0 2 4 6 8 10 12

Angle of Attack

Cl

Cmu=0.1657

Cmu=0.111

Cmu=0.0566

Cmu=0.0

Leading Edge Stall

Time History of Lift Coefficient for the Unblown Case

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0.72

0.74

0.76

0.78

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0.82

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0.88

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0 1 2 3 4 5 6 7 8 9 10

Time (msec)

Clt = 1.578693 msec

t = 4.128484 msec t = 6.678274 msec

• The Vortex Shedding Frequency is about 400 Hz for this case (Strouhal No. = 2.828).• In the acoustic experiments, two frequencies were measured (Strouhal No. = 1.67, 4.73).

Pressure Contours for the Unblown Case

Stream Function Contours when Blowing is Applied

Comparison with Conventional High-lift Systems

• The figures show the high-lift systems configuration with a 300 fowler flap and the body-fitted grid.• The results are obtained with a 2-D multi-block version of the present method.

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Lift Coefficients

Drag

Coe

ffici

ents

Multi-element Airfoil at Different Angle of Attack

30 Degree Flap CCW Airfoil, Cd not corrected

30 Degree Flap CCW Airfoil, Cd corrected by Cd+Cmu

• For the multi-element airfoil, high lift is achieved by changing the angle of attack; For the CCW airfoil, high lift is achieved by changing the blowing coefficient while the angle of attack is fixed at 0 degrees.

Pulsed Jet Results• Pulsed jet studies were done to answer:

---- Can pulsed jets be used to achieve desired increases in the lift coefficient at lower mass flow rates relative to a steady jet? ----What is the optimum wave shape for the pulsed jet, ie, how should it vary with time? ---- What are the effects of the pulsed jet frequency on the lift coefficient?

• Sinusoidal and Square wave form variations were considered. Sinusoidal forms were found ineffective.

• tfFCCtC ,0,0,

Momentum Coefficient Variation with Time for Pulsed Jet Square Wave Form, Frequency = 40 Hz

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0.44 0.45 0.46 0.47 0.48 0.49 0.5

Time (sec)

C

Dt = 0.025002 (sec)

C

sec40/1t

Variations of Incremental Lift Coefficient with Time-Averaged Momentum Coefficient, CComparison of Steady Jet with Pulsed Jet

0

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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Time-Averaged Momentum Coefficient, C0

Cl

Steady JetPulsed Jet , f = 40HzPulsed Jet, f = 120 HzPulsed Jet, f = 400 Hz

• Cl= Clblowing- Clnonblowing

•Steady jet is continuously on, while the pulsed jet is operational only half the time during each cycle.

Variations of Incremental Lift Coefficient with Time-Averaged Mass Flow Rate

Comparison of Steady Jet with Pulsed Jet

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0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016

Time Averaged Mass Flow Rate (slugs/sec)

C

l

Steady JetPulsed Jet , f = 40 HzPulsed Jet ,f = 120 HzPulsed Jet, f = 400 Hz

jet2jet VmandVC

• The average mass flow rate of a pulsed jet is just about 70% of the steady jet at the same C0 value.

Variation of Efficiency (Cl/(Cd+C)) with Time-Averaged Momentum Coefficient, CComparison of Steady Jet with Pulsed Jet

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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Time-Averaged Momentum Coefficient, C

Cl/(C

d+C )

Steady JetPulsed Jet , f = 40 HzPulsed Jet , f = 120 HzPulsed Jet, f = 400 Hz

Average Lift Coefficient Vs. Frequency For Pulsed JetThe Time-Averaged Momentum Coefficient is 0.04

0

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0 40 80 120 160 200 240 280 320 360 400Frequency (Hz)

Cl

Pulsed Jet, Ave. Cmu=0.04

Steady Jet, Cmu=0.04

0

Strouhal Number ( f * Chord / Vinf)

2.8281.414

Pulsed Jet at 400 Hz requires only 73% of the steady jet mass flow rate while achieves 95% of the steady jet lift.

Effect of Pulsed Jet Frequency• High Frequencies were more effective.

• This is explained as follows:

• When the jet is turned off, the beneficial Coanda effect persists for several chord lengths of travel.

• If a new cycle starts soon, the Coanda effect quickly reestablishes itself.

Stream Lines around the Airfoil Trailing Edge Pulsed Jet Frequency = 120 Hz

Stream Lines around the Airfoil Trailing Edge Pulsed Jet Frequency = 400 Hz

Average L/D (Efficiency CL/(CD+C )) Vs. Frequency For Pulsed Jet The Time-Averaged Momentum Coefficient is 0.04

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0 40 80 120 160 200 240 280 320 360 400Frequency (Hz)

CL/

(CD

+C

Pulsed Jet, Ave. Cmu=0.04

Steady Jet, Cmu=0.04

Strouhal Number ( f * Chord / Vinf)

0 2.8281.414

• CCW concept is an extremely effective way of achieving high CLmax, without the drawbacks of conventional high-lift systems.

• The steady jet calculations are in good agreement with the measurements. It is seen that blowing can successfully eliminate the vortex shedding, a potential noise source.

• The pulsed jet configuration can give larger increments in lift coefficient compared to the steady jet at the same mass flow rate.

• The pulsed jet performance improved at higher pulse frequencies.

Preliminary Conclusions

Proposed Work1. Effects of Tangential Blowing on Leading Edge Stall

• Slats are often used as a way of suppressing leading edge stall at high angles of attack; the use of slats creates new noise sources and wing complexities; leading edge tangential blowing is an effective way of eliminating leading edge stall without using of slats.

Leading Edge Blowing Trailing Edge Blowing

Proposed Work (cont’d)2. Effects of Tangential Blowing for Flap Edge Vortex Reduction (Three Dimensional Application)

The Lift Distribution along Span for Traditional Wing-Flap Configurations

The Lift Distribution along Span for CCW Wing-Flap Configurations

• Circulation Control Jets are used on the main wing and on the flap edge to reduce the flap edge vortex strength.

Questions ?